The Biology of White Markings

"AKG, from my (admittedly somewhat limited) understanding of dog coat genetics, the white marks frequently seen on Vizsla chests and toes is not something being thrown in from pointers, and is not necessarily hereditary. The presence of these marks is due to incomplete migration of melanocytes during development. This is why you can have pups born with white marks on the chest, even though the dam, sire, and previous generations won't have had the white marks.

Biology time (I'm a molecular biologist--bear with me)! Melanocytes, which are cells that produce pigment (such as the baguette/golden rust/whatever you want color of our Vs), migrate from the neural crest during embryonic development. The neural crest is basically a precursor to the spinal cord. The cells have to migrate the farthest to reach places like the chest or the toes (those aren't formed yet, but the tissue that will become those structures is). Sometimes during development there is a delay--maybe the mom got a tiny cold, something that wasn't even symptomatic. Maybe something stressed her and her developing pups. Maybe one developing pup was in a weird, less-than-ideal spot in the womb, while the others were unaffected. Or there could be some other reason that scientists and breeders have not yet elucidated. But for whatever reason, the migration might be delayed, resulting in some areas of the developing dog that lack melanocytes, and thus lack pigmentation in their fur that grows from that area. At a certain point in development, if the tissue lacks melanocytes, it will lack them forever, so if migration was delayed and the cells never got there...boom. White. This is why you often see those white spots on the chest and/or toes. Whether or not the rate of melanocyte migration is hereditary remains to be seen. 

Chloe has a bit of white on her chest

For now, these marks are considered incidental, which is why a small amount is permissible on the chest and/or toes in the conformation ring. The marks have no influence on other qualities of the dog, such as sound body structure, trainability, eagerness, temperament, and/or hunting ability, and so they would not be a limiting factor in the field."

Generously allowed to be posted to RBD by a fellow member of the Hungarian Vizlsa Forum who goes by Redrover.  Thanks.